I installed the Eclipse IDE for Java Developers (Galileo Packages (based on Eclipse 3.5 SR1)) in my computer.
I try to fine the SWT document,
in this page, http://www.eclipse.org/swt/docs.php , he say:

"The Eclipse Help system contains good solid documentation for SWT in the Platform Plug-in Developer Guide. To get there in Eclipse, select
Help > Help Contents > Platform Plug-in Developer Guide."

I suspect that the Eclipse IDE for Java Developers release does not include
this documentation because it's assumed that this release would not be used
for writing eclipse plugins. The full eclipse releases do contain this
documentation, they are available fromhttp://download.eclipse.org/eclipse/downloads/ .